Step 4: Install An Ac Junction Box - enphase M250 Installation And Operation Manual

Step 4: Install an AC Junction Box

DANGER: Risk of electric shock. Be aware that installation of this equipment includes risk of electric shock. Do
not install the AC junction box without first removing AC power from the Enphase System.
WARNING: Only use electrical system components approved for wet locations.
WARNING: Do NOT exceed the maximum number of microinverters in an AC branch circuit as listed on page
9 of this manual.
a. Install an appropriate junction box at a suitable location on the mounting system. You can
centre feed the branch, or you can install the junction box at the end of a row of PV modules.
Best Practice: Centre-feed the branch circuit to minimise voltage rise in a fully-populated branch. This practice
greatly reduces the voltage rise as compared with an end-fed branch. To centre-feed a branch, divide the
circuit into two sub-branch circuits protected by a single overcurrent protection device (OCPD).
b. Size the AC cable/wire size to account for voltage drop. Select conductor diameter based on
the distance from the beginning of the microinverter AC branch circuit to the breaker in the
AC mains.
All components of system wiring must be considered, including internal voltage drop within
the length of Engage Cable. Typically, three wire sections and several wire terminations
must be quantified. There is also some resistance associated with each circuit breaker. As
all of these resistances are in series, they add together. Since the same current is flowing
through each resistance, the total voltage drop is total current times the total resistance. For
a single-phase system, the total resistance is equal to two times the one-way resistance. For
a three-phase system, each of the three line currents and resistances must be calculated.
Standard guidelines for voltage drop on feeder and AC branch circuit conductors might not
be sufficient for microinverter AC branch circuits that contain the maximum allowable
microinverters. This is due to high inherent voltage rise on the AC branch circuit.
For more information, refer to our Technical Briefs on Voltage Drop at
http://www.enphase.com/support.
c. Provide an AC connection from the AC junction box back to the electricity network
connection using equipment and practices as required by local regulations.
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M-Series Microinverter Installation and Operation
141-00024 Rev 02b